Cognitive radios (CR) utilize a variety of co-existence techniques in order to attempt to operate successfully along with existing wireless communication networks or architectures. The CR concept is generally intended to enable frequency band sharing and reuse with incumbent users and/or other CR devices. The manner by which CR performance can be increased or extended, via the use of advanced cognitive techniques, is of current interest in the communications arena.
Wireless systems utilizing cognitive radio techniques are intended to allow a network or a wireless node to change its transmission or reception parameters to communicate efficiently and utilize spectrum on a secondary basis without interfering with incumbent users or other CR devices operating in the same frequency band. However, due to the wide variety of incumbent receiver equipment providers on the market and different field operating conditions, controlling the operating parameters of CR systems becomes a very challenging task. The mobility of many CR devices, such as portable radios, exacerbates the problem.
The unlicensed use of locally unused television white space (TVWS) spectrum is particularly challenging and comes under the regulation of the Federal Communications Commission (FCC) in the U.S. Currently the FCC is developing regulations including the use of geo-location database enabled CR TVWS devices and sensing-only CR TVWS devices.
Geo-location database enabled CR devices determine their own location, and from the geo-location database, determine the maximum allowed transmit power level that avoids causing interference to licensed incumbent (for example, TV) receivers. These CR power level computations are, as the FCC has currently proposed, based on receiver co-channel and adjacent channel interference protection ratios only. However, these co-channel and adjacent channel protection ratios do not adequately ensure avoiding interference to incumbent TV receivers.
For sensing-only based CRs that have no geo-location information or connection to a database, the radios must operate based on sensed signal information alone. A large class of TVWS devices will utilize only spectral sensing techniques to determine open spectrum. A need thus exists to ensure these sensing-only radios do not interfere with licensed incumbents.
Accordingly, there is a need for a technique to ensure that licensed incumbent receivers are adequately protected from all forms of unwanted CR interference, particularly in the arena using TVWS devices.
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